Siloxane containing thermoplastic elastomers

ABSTRACT

Block copolymers of polydiorganosiloxane blocks and polystyrene blocks are thermoplastic elastomers useful as coating materials and film formers with gas permeability.

United States Patent Saam et al.

[ SILOXANE CONTAINING THERMOPLASTIC ELASTOMERS [72] Inventors: John C.Seam; Frederlck W. G. Feamn, both of Midland, Mich.

[73] Assignee: Dow Corning Corporation, Midland, Mich.

[221 Filed: Aug. 25, 1970 21 Appl. No.: 66,893

[52] U.S. Cl ..260/827, 55/522, 117/161 ZA,

260/23 S, 260/33.6 SB, 260/935 R [51] Int. Cl. ..C08g 47/10, C08f 33/08[58] Field of Search 2 /827 [56] References Cited UNITED STATES PATENTS3,483,270 12/1969 Bostick ..260/827 [151 3,678,126 51 July 18,1972

Primary Examiner-Sanuel H. Blech Attorney-Robert F. Fleming, Jr.,Laurence H. Hobey, Harry D. Dingman and Roger H. Borrousch [57] ABSTRACTBlock copolymers of polydiorganosiloxane blocks and polystyrene blocksare thermoplastic elastomers useful as coating materials and filmformers with gas permeability.

7Chims,NoDrawings SILOXANE CONTAINING THERMOPLASTIC ELASTOMERS Thisinvention relates to block copolymers which are thermoplasticelastomers.

Block copolymers of various kinds are known in the polymer art. Each ofthe block copolymers described in the art are said to have some specialadvantage or property. It is an object of this invention to provide ablock copolymer which is a thermoplastic elastomer. This object andothers will become apparent from the following detailed description ofthe present invention.

This invention relates to a thermoplastic-elastomer consistingessentially of a block copolymer of the formula in which each R is amonovalent radical selected from the group consisting of methyl, ethyl,phenyl and vinyl, each R is selected from the group consisting of ahydrogen atom and a methyl radical, R is a divalent hydrocarbon radicalhaving from two to 30 inclusive carbon atoms, each R is a monovalentradical selected from the group consisting of methyl, ethyl, propyl,butyl, phenyl and 3,3,3-trifluoropropyl, each A is a monovalent radicalselected from the group consisting of a hydrogen atom and R Si radicals,m is an integer of from to l inclusive, w and y have a value such thatthe molecular weight of is greater than 7000, x and 2 have a value suchthat the block copolymer has 65 to 85 inclusive weight percent R SiO, gis an integer of from 0 to l inclusive, and n has a value greater than1, there being present less than 5 weight percent freepolydiorganosiloxane and there being present less than weight percentfree polystyrene.

The block copolymers of the present invention can be prepared bypolymerizing styrene or alpha-methyl styrene or mixtures thereof in anorganic solvent solution with a dilithium organic compound of theformula (R")Li where R" is a divalent hydrocarbon radical having fromtwo to inclusive carbon atoms such as illustrated in the followingcompounds such as dilithiostilbene, 1,4-dilithiobenzene,1,5-dilithiopentane, 1,5-dilithionaphthalene andl,2-dilithio-l,3,3-triphenylpropane. The amount of dilithium organiccompound used per amount of vinyl containing organic monomer willdetermine the size of the organic block. The smaller the amount ofdilithium organic compound per given amount of styrene oralpha-methylstyrene, the greater the number of polymerized styrene oralpha-methylstyrene units in the resulting polymer. The amount of thedilithium organic compound used can be readily approximated by takingthe value obtained by dividing the weight of the styrene or alphamethylstyrene to be used by the molecular weight of the polystyrene orpoly-alpha-methylstyrene block desired. The results provide the numberof moles of dilithium organic compound which is to be used. Since thereaction goes to almost 100 percent conversion and if the undesirableimpurities have been carefully removed, the number average molecularweight obtained will be very close to the desired molecular weight usedin determining the number of moles of dilithium organic compound to beused. It is to be understood that under certain conditions the resultscan deviate somewhat from those calculated, since the percent conversioncan vary.

The reaction between the dilithium organic compound and the styrene andalpha-methylstyrene should be carried out under conditions free fromcontaminations such as water, air, oxygen, inhibitors, acidicimpurities, greases and the like. The

2 mixture of styrene or alpha-methylstyrene and the dilithium organiccompound in solvent solution are maintained at a temperature between thereflux temperature of the mixture and the freen'ng point of the mixtureuntil the styrene or alphamethylstyrene has polymerized. Whenalpha-methylstyrene is the major monomer to be used, it is'desirable tocarry out the polymerization below 40" C. and thereafter to add smallamounts of styrene and continue the polymerization to provide smallpolystyrene segments on the poly-alpha-methylstyrene. Since thehexaorganocyclotrisiloxane does not readily polymerize with the lithiumended polymers below 40 C. and since the lithium endedpoly-alpha-methylstyrene tends to depolymerize above 40 C., the smallsegments of polystyrene on the poly-alpha-methylstyrene allow thereaction mixture to be warmed above -40 C. without depolymerization.Further details describing this method can be found in our copendingapplication filed concurrently herewith Ser. No. 66,891, filed Aug. 25,1970, and entitled A Method of Preparing a Block Copolymer Containing aPoly- Alpha-Methylstyrene Block and a Polydiorganosiloxane Block andBlock Copolymers Prepared Thereby.

The reaction product from the reaction of the dilithium organic compoundand styrene, for example, is a lithium terminated polymer of thefollowing formula wherein y and w are the number of styrene units in thepolymer and R" is the residue from the dilithium organic compound. lnthis case g is 1. When the electron transfer polymerization method isused to polymerize the styrene or alpha-methylstyrene, g is 0 since noresidue results in the polymeric product. The electron transferpolymerization methods well known in the art as described in US. Pat.Nos. 2,985,594; 3,134,745 and 3,458,491 are hereby incorporated byreference to describe the process.

To the lithium terminated polymer solution, hexaorganocyclotrisiloxanein solvent solution is added in an amount sufficient to provide at leastone hexaorganocyclotrisiloxane molecule per each lithium end. Theaddition should be carried out so that there is no exposure topreviously stated impurities. The resulting product would be, for themost part, a polymer of the formula wherein styrene is used forillustrative purposes,

where R, R", y and w are defined above and a and b are each from 1 to 3inclusive. The reaction is held at a temperature between 50 C. and nogreater than the reflux temperature of the mixture. After sufficienttime has elapsed, which is at least 30 minutes to 4 hours and which isrecognizable by the disappearance of the color characteristic forlithium ended organic polymers, additional hexaorganocyclotrisiloxane insolvent solution and a polymerization promoter preferably in an amountof at least one weight percent based on the weight of the mixture isadded to the lithium ended silicon-containing copolymer.Hexaorganocyclotrisiloxane is added in an amount necessary to providethe desired siloxane block size such that the block copolymer containsfrom 65 to weight percent R SiO units. The reaction mixture ispreferably heated to reflux for 3 to 4 hours to increase the reactionrate. The reaction, however, can be carried out between -50 'C. and

the reflux temperature of the mixture for at least 30 minutes orgreater. The resulting product has a formula where R, R, R", y and w aredefined above and x and 2 have values such that the block copolymer hasfrom 65 to 85 weight percent R SiO units. The lithium ended blockcopolymer can be condensed directly, terminated with silanols byreaction with a protonic material such as acetic acid and then condensedor by reaction with R"' SiCl This lithium ended block copolymer is thenreacted with sufficient R"' SiCl to couple the molecules of blockcopolymer together and increase the molecular weight sufficiently toprovide a block copolymer of the formula where R, R', R", y, w, x and zare defined above, n has a value greater than 1, m is or 1, and each R'is a monovalent radical of methyl, ethyl, propyl, butyl, phenyl or3,3,3- trifluoropropyl. The lithium atoms in this polymer can bereplaced by hydrogen atoms by washing the polymer with water and at thesame time removing the lithium chloride formed or acetic acid can beadded to replace the lithium atoms with hydrogen atoms. iftriorganosilyl ended polymers are desired, R SiCl can be added whereinthe lithium atoms are replaced by R;,Si groups.

The R"' SiCl compounds can be illustrated by dimethyldichlorosilane,methylphenyldichlorosilane, methyl-3,3,3- trifluoropropyldichlorosilane,ethylmethyldichlorosilane, diethyldichlorosilane,butylmethyldichlorosilane and the like.

The styrene, alpha-methylstyrene and the organic solvents should bewashed, dried and/or distilled prior to use to remove any impuritiessuch as water, inhibitors and the like. Suitable organic solventsinclude the hydrocarbon solvents which are solvents for the styrene andalpha-methylstyrene, such as cyclohexane, toluene, benzene, n-hexane,mineral spirits, methylcyclohexane, xylene, n-butane, n-heptane,isooctane and cyclopentane.

The organic solvent for the solution of the hexaorganocyclotrisiloxanecan be any of those stated above for use during the polymerization ofthe styrene and alpha-methylstyrene. The polymerization promoter can be,for example, tetrahydrofuran and bis( 2-methoxyethyl)ether.

In the block copolymer of the present invention, R can be methyl, ethyl,phenyl or vinyl. The diorganosiloxane units, therefore, can beillustrated by dimethylsiloxane, diphenylsiloxane, methylphenylsiloxane,diethylsiloxane, ethylmethylsiloxane and methylvinylsiloxane.Preferably, R is methyl.

When A is a triorganosilyl group, R Si-, triorganochlorosilanes areconveniently used to endblock the block copolymers. Illustrative ofthese triorganochlorosilanes are trimethylchlorosilane,phenyldimethylchlorosilane, methylphenylvinylchlorosilane,dimethylvinylchlorosilane, dimethylethylchlorosilane and the like.

The block copolymers of the present invention arethermoplastic-elastomers. These materials have good elastomericproperties at room temperature in the uncured state, however, uponheating to a temperature such as 80 to 100 C. the material becomesthermoplastic. Therefore, these thermoplastic elastomers are elastomersat temperatures from below room temperature to some temperature above 50C. in the uncured and unfilled state. The thermoplastic-elastomers canbe fabricated in the same manner as ordinary thermoplastics, since theyare organic solvent soluble, have softening and melting ranges. Thesethermoplastic elastomers can readily be fabricated and molded attemperatures above 150 C. or at lower temperatures from solutions. Sincethese thermoplastic elastomers do not need to be cured to obtain theirexcellent properties, they can be put into solution or molded repeatedlywithout loss of property. These thermoplastic elastomers are gaspermeable and film formers and thus, gas permeable membranes can be madefrom them. The thermoplastic-elastomers have good electrical propertiesand good weatherability. These properties provide excellent elastomericprotective coatings and electrical insulation which can be applied fromthe polymer melt or solution.

The thennoplastic-elastomers rapidly lose their elastomeric propertywhen the polymer mixture contains 5 weight percent or more freepolydiorganosiloxane or contains 10 weight percent or more freepolystyrene or poly-alpha-methylstyrene. Therefore, thethermoplastic-elastomers of the present invention must have less than 5weight percent free polystyrene or poly-alpha-methylstyrene. Freecopolymers of styrene and alpha-methylstyrene are also considered withinthese limitations.

The following examples are illustrative only and should not be construedas limiting the present invention which is properly delineated in theclaims.

EXAMPLE I A solution of 0.0133 moles of dilithiostilbene in 26.6 ml. oftetrahydrofuran was added to a solution of g. of purified styrene in 800ml. of pure dry benzene in a dry nitrogen atmosphere. The temperature ofthe polymerization was held at 25 to 30 C. with cooling. After two hoursa one-fourth aliquot of a dry solution of 420 g.hexamethylcyclotrisiloxane in 2,100 ml. of purified toluene was addedwithout exposure to the atmosphere. The highly viscous mixture wasvigorously stirred until the characteristic orange color of the living"polymer disappeared. At this point the mixture passes through a thickgel phase and then forms a highly viscous solution. The remaininghexamethylcyclotrisiloxane solution was added, followed by ISO ml. ofpurified (CH OCH Cl-l O. After 8 hours polymerization, the resultingpolymer had a formula Calls Calls CoHr CH5 with a molecular weight asdetemiined by membrane osmometry of 45,100 (calculated M 45,000), thesum of y and w was about 130 and 32.6 weight percent was polystyreneblocks and 67.4 weight percent was polydimethylsiloxane blocks. To thesolution of the above block copolymer, 2.16 ml. of CF Cl-l Cl-l(ClI,-,)SiCl was added with agitation. After 18 hours the solution wasfiltered, washed with water and the solvent was removed in a vacuum at80 C. The molecular weight of the resulting block copolymer was 257,000by membrane osmometry, and the formula was CuHg dig CHgCHzC F: n

[OSi (CH3)211(CHCII7) CHCH (CH2CH)w[(CH3)2 SiOLH C5115 Cons CsHs 0on5where n was 4.7. The tensile strength at break of the above blockcopolymer on compression molded test bars was 1,300 p.s.i., theelongation at break was 490 percent and the Die B tear strength wasp.l.i. The thermoplastic-elastomer had a tensile strength at yield of240 p.s.i. and an elongation at yield of 3 percent with only a smalltension set.

EXAMPLE 2 The procedure of Example 1 was used to prepare blockcopolymers as defined by the formula describing the con- For comparativepurposes only.

The electrical properties for block copolymer No. 2 were as follows: adielectric constant at Hertz of 2.63, a dissipation factor at 10" Hertzof 0.00024, a volume resistivity of 1.3 X l0 ohm. -cm. and a dielectricstrength of 530 volts/mil. The above block copolymers had a gaspermeability for oxygen of 25 X 10' cm -cmlcm -sec. cm Hg and fornitrogen of 1 1.1 X 10* cm cm/cm -sec cm Hg.

EXAMPLE 3 The following procedures were carried out by removing anywater acidic materials, oxygen and inhibitors from the inwas atransparent elastomer.

EXAMPLE 4 The block copolymer of Example 1 was solvent fractionated intodifferent molecular weight fractions. The various fractions and thephysical properties of each fraction were as shown in Table 11.

TABLEH Wt. Polydi- Tensile Elong- Molemethyl- Strength ation Fraccularsiloxane at break, at break,

tion Wt. n Blocks p.s.i.

" "Uncondensed prepolymer.

* "Unfractionated block copolymer.

That which is claimed is:

l. A thermoplastic-elastomer consisting essentially of a block copolymerof the formula gredients. A solution of 0.012 moles of dilithiostilbenein 20 ml. of tetrahydrofuran was added to a solution of g. ofalpha-methylstyrene in 500 ml. of tetrahydrofuran. The resultingsolution was cooled to 70 C. and held at this temperature for 30 minutesduring which time the alpha-methylstyrene was polymerized. To theresulting mixture, 4.55 g. of styrene was added. After 5 minutes, thestyrene had polymerized. Thereafter, the mixture was allowed to warm toambient temperature. No alpha-methylstyrene monomer was detected in thewarmed mixture. To the warmed mixture, 140 g. ofhexamethylcyclotrisiloxane in 515 ml. of benzene was added. After 4hours 95 percent of the hexamethylcyclotrisiloxane was consumed. Thepolymerization was terminated with the addition of 5 ml. of acetic acid.The mixture was thereafter washed with 100 ml. of a 20 weight percentsolution of sodium bicarbonate in water. The solution was washed withwater until neutral and the block copolymer was then precipitated byadding the solution to 3,000 ml. of ethanol. The precipitated polymerwas washed twice with ethanol and then dried at 40 C. and 1 mm of Hg for24 hours. 156 g. of the block copolymer was recovered having 83 weightpercent polydimethylsiloxane block and 17 weight percentpolyalpha-methylstyrerte-styrene block, based on silicon analysis. Nofree .polydimethylsiloxane was found in the block copolymer.

To 50 g. of the above block copolymer in 500 ml. of cyclohexane, 0.5 m1.of stannous octoate was added. The solvent was removed and the resultingpolymer was heated at 140 C. at 1 mm of Hg for 24 hours. The product wascooled, dissolved in 500 ml. of toluene and then precipitated by addingvthe toluene solution to 2,000 mi. of ethanol. The precipitated blockcopolymer was washed with ethanol and then dried at 40 C. at 1 mm of Hgfor 24 hours. The product CrHs CBHS in which each R is a monovalentradical selected from the group consisting of methyl, ethyl, phenyl andvinyl, each R is selected from the group consisting of a hydrogen atomand a methyl radical, R" is a divalent hydrocarbon radical having fromtwo to 30 inclusive carbon atoms, each R is a monovalent radicalselected from the group consisting of methyl, ethyl, propyl, butyl,phenyl and 3,3,3-trifluoropropyl, each A is a monovalent radicalselected from the group consisting of a hydrogen atom and R Si radicals,m is an integer of from 0 to 1 inclusive, w and y have a value such thatthe molecular weight of is greater than 7,000, x and 1 have a value suchthat the block copolymer has 65 to 85 inclusive weight percent R SiO, gis an integer of from 0 to 1 inclusive, and n has a value greater than1, there being present less than 5 weight percent freepolydiorganosiloxane and there being present less than 10 weight percentfree polystyrene.

2. The thermoplastic-elastomer in accordance with claim 1 in which R isa hydrogen atom.

3. The thermoplastic-elastomer in accordance with claim I in which R isa methyl radical.

4. The thermoplastic-elastomer in accordance with claim 2 in which R isa methyl radical and A is a hydrogen atom.

5. The thermoplastic-elastomer in accordance with claim 3 in which R isa methyl radical and A is a hydrogen atom.

6. The thennoplastic-elastomer in accordance with claim 4 in which 3 isl.

7. A gas permeable membrane consisting essentially of a film of thethermoplastic-elastomer according to claim I.

i i i t

2. The thermoplastic-elastomer in accordance with claim 1 in which R''is a hydrogen atom.
 3. The thermoplastic-elastomer in accordance withclaim 1 in which R'' is a methyl radical.
 4. The thermoplastic-elastomerin accordance with claim 2 in which R is a methyl radical and A is ahydrogen atom.
 5. The thermoplastic-elastomer in accordance with claim 3in which R is a methyl radical and A is a hydrogen atom.
 6. Thethermoplastic-elastomer in accordance with claim 4 in which g is
 1. 7. Agas permeable membrane consisting essentially of a film of thethermoplastic-elastomer according to claim 1.